Date: Sat, 28 Nov 2009 13:00:50 +0530
From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
To: Veaceslav Falico <vfalico@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Paul Mackerras <paulus@samba.org>,
       Alexey Dobriyan <adobriyan@gmail.com>,
       Christoph Hellwig <hch@infradead.org>,
       "Frank Ch. Eigler" <fche@redhat.com>, Ingo Molnar <mingo@elte.hu>,
       Peter Zijlstra <peterz@infradead.org>,
       Roland McGrath <roland@redhat.com>, linux-kernel@vger.kernel.org,
       utrace-devel@redhat.com,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: powerpc: fork && stepping (Was: [RFC,PATCH 0/14] utrace/ptrace)
Message-ID: <20091128073049.GD23108@in.ibm.com>
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On Fri, Nov 27, 2009 at 06:46:27PM +0100, Veaceslav Falico wrote:
> On Thu, Nov 26, 2009 at 11:37:03PM +0100, Oleg Nesterov wrote:
> >
> > Could you look at this
> >
> >   ptrace-copy_process-should-disable-stepping.patch
> >   http://marc.info/?l=linux-mm-commits&m=125789789322573
> >
> > patch? It is not clear to me how we can modify the test-case to
> > verify it fixes the original problem for powerpc.
> 
> I modified the test-case, it confirms that
> ptrace-copy_process-should-disable-stepping.patch fixes the
> problem with TIF_SINGLESTEP copied by fork() on powerpc.
> 
> Probably we need a similar fix for step-fork.c in ptrace-tests.
> 
> Modified the original testcase to call fork via syscall(__NR_fork),
> to avoid the looping inside libc's fork() on powerpc.
> The parent singlesteps until he sees that the child has forked, after
> that the parent PTRACE_CONTs until the child exits.

Thanks Veaceslav. This works:

Index: ptrace-tests/tests/step-fork.c
===================================================================
--- ptrace-tests.orig/tests/step-fork.c
+++ ptrace-tests/tests/step-fork.c
@@ -29,6 +29,7 @@
 #include <unistd.h>
 #include <sys/wait.h>
 #include <string.h>
+#include <sys/syscall.h>
 #include <signal.h>

 #ifndef PTRACE_SINGLESTEP
@@ -78,7 +79,7 @@ main (int argc, char **argv)
        sigprocmask (SIG_BLOCK, &mask, NULL);
        ptrace (PTRACE_TRACEME);
        raise (SIGUSR1);
-       if (fork () == 0)
+       if (syscall(__NR_fork) == 0)
          {
            read (-1, NULL, 0);
            _exit (22);

Oleg,
With the above patch applied, syscall-reset is the only failure I see on
powerpc:

errno 14 (Bad address)
syscall-reset: syscall-reset.c:95: main: Assertion `(*__errno_location
()) == 38' failed.
unexpected child status 67f
FAIL: syscall-reset
...
========================================
1 of 40 tests failed
(11 tests were not run)
Please report to utrace-devel@redhat.com
========================================

Ananth
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